Scrap aluminum cans: recycling

From scrap aluminum cans to the new banks

Recycling scrap aluminum cans in the new banks is considered a remarkable example of almost waste-free production process. Exactly recycling scrap aluminum cans He played a major role in the rapid growth of the market of aluminum cans for beer and carbonated drinks.

In the manufacture of aluminum from aluminum scrap consumed 95 % less energy, than at its smelting of mineral ores. The process of recycling aluminum scrap gives only 5 % emissions from, which destroy the earth's ozone layer, than in the production of primary aluminum [4].

In the world sells more than 350 billion aluminum cans. However, not all banks enter the scrap. The share of scrap in the total volume of aluminum cans is:

  • in Sweden – 90 % aluminum cans,
  • in USA – to 70 %,
  • in Australia, Canada, Japan and China - about 80 %,
  • in the whole world - a little more than 50 %.

V 2017 It was processed in Europe 74,5 % used aluminum cans of beer and beverage. As was the case in various European countries, see. the chart pattern 1 [4]. A typical plant for processing aluminum cans into ingots for rolling aluminum sheet, which is used to make new cans, shown in Figure 2.

Figure 1 – The proportion of recycled aluminum cans
for European countries [4]

Figure 2 – Plant for processing scrap aluminum cans
into rolled ingots for the manufacture of new cans [3]

A small portion of the scrap aluminum cans melted in conventional melting furnaces or rotary, and it is, primarily, for production of casting alloys.

Plain remelting of aluminum waste cans gives on average the following composition of aluminum [2]:

  • Si - 0,26 %
  • Fe - 0,40 %
  • Cu - 0,20 %
  • Mn - 0,86 %
  • Mg – 1,22 %
  • Ti - 0,04 %
  • other - Al.

“Aluminum” such chemical composition is well within the range of chemical composition of alloys 3004 and 3104 (cm. table below), which is used for making the can body. Therefore, the vast majority of metal from scrap aluminum cans – near 80 % – returns to producers of new cans.

The following are the common approaches to the processing of scrap aluminum cans, when it is used again for manufacturing cans. similar, sometimes very complex, technology is used in many plants in the US and Western Europe.

Alloys of aluminum cans

Good to know, that aluminum cans are made from several different aluminum alloys and only from them (table):

  • The housing banks apply aluminum alloy 3004 or aluminum alloy 3104, which are very close in chemical composition: manganese and magnesium on average 1 %, copper - up 0,25 % and iron - up 0,7-0,8 %.
  • Cover jars made of alloy 5182. This magnesium alloy has 4-5 %, and manganese - 0,20-0,50 %.
  • Key for opening bank gives the smallest contribution to the total weight of the banks. It is made of an alloy 5042 with magnesium 3-4 % and manganese - 0,20-0,50 %.


Shredding scrap aluminum cans

Typically aluminum cans come to be melted in the form of briquettes weighing 400 kg and a density of no more than 500 kg / m3. These briquettes are easy to transport, but it is not suitable for direct loading into a furnace to be melted down into materials, which will be used to manufacture new cans. Therefore, these briquettes are subjected to shredding and sorting, To make sure, that they are no liquids or hazardous materials. It is very important to ensure the safety and security of casters foundry equipment. To do this, use the special pulverizer – shredder.

The sorting of aluminum scrap

From this shredder scrap particulate passes through a magnetic separator, which removes impurities magnetic steel. After the magnetic separator scrap passes air knife, where separated material, which are heavier than aluminum: lead, zinc and stainless steel. After the operation of grinding and sorting, shredded and sorted aluminum cans (or that, what is left of them) go to the equipment for varnish removal.

"Delakirovanie" scrap aluminum cans

Apply two approaches continuous thermal Removers. One is based on relatively long storage shredded aluminum scrap at a certain temperature, and the other - on the short heating cycle, with a gradual increase in temperature to just below melting temperature aluminum scrap.

In the first case used a conveyor oven, wherein shredded aluminum cans pass through the chamber at a temperature of about 520 ° C. This chamber contains the combustion products of varnish, which is diluted with air to create a positive atmosphere to remove varnish.

The second approach used a rotary furnace with a complicated recirculation of combustion products. last stage temperature - about 615 ° C, which is very close to the temperature of the onset of melting in aluminum-magnesium alloys, from which covers are usually made (alloy 5182) and keys for opening (alloy 5054) beer cans.

Both systems can be a problem, which lead to incomplete removal of varnish. If the temperature is too low or the treatment time is too short, the aluminum surface is black resinous coating. This leads to the risk of fire when scrap melting and excessive loss of metal due to burn. If the temperature is too high or the treatment time is too great, this leads to significant oxidation of scrap and also leads to an increased loss of metal.

Separating aluminum alloys

Hot, "Delakirovanny" scrap aluminum then flows into separator chamber thermomechanical. In this chamber the desired temperature and nonoxidizing. In her cover of an alloy of cans 5182, and alloy keys 5054, light subjected to mechanical stress, as a result of which they are broken down into tiny pieces along the grain boundaries. The whole process is based on the, that under the influence of a narrow temperature range only soften the grain boundaries. These small fragments of alloys 5181 and 5054 continuously screened and directed to the furnace for remelting caps, and the remaining aluminum scrap - into the furnace for remelting can bodies.

The melting of aluminum scrap

For melting aluminum cans generally used special ovens. Upon melting, a substantial amount of slag - metal mixture, oxides and other contaminants. This slag contains a lot of gas, so good swimmer on top of the melt. It is removed and is sent to metal recovery therefrom. Typically, slag weight is about 15 % from scrap bootstrapping. From this special furnaces melt transmitted in a continuous melting furnace, which additionally charged with a large aluminum scrap and primary unalloyed aluminum to produce the desired volume and the approximate chemical composition of a given alloy.

Treatment of molten aluminum

From a continuous melting furnace melt is supplied to the holding furnace. There produce melt podshihtovku - make the necessary additives and metal ligatures to obtain the desired chemical composition of the alloy. In the same furnace produce melt processing, for example, purging with an inert gas to remove unwanted non-metallic inclusions.

ingot casting and rolling the sheet

Clean and with the desired chemical composition of the melt is cast into ingots weighing 15 tonnes. When ingot casting and rolling the ingot to sheet breakage may take up 40 % initial amount of metal melt. This occurs when trimming end, edges and similar operations. This is called internal scrap. He is a very valuable, since its chemical composition is identical to specify. He was immediately sent for remelting ingots manufacturer.

Aluminum cans

Aluminum tape for the shells and lids of cans supplied by the manufacturers of cans. As a result of the process production of aluminum cans near 20 % aluminum tape (or 13 % from the initial melt) is returned to the manufacturer of ingots in the form of industrial waste - the remnants of sheets with holes in place of cut blanks for bodies and lids of cans. Generally, near 55 % amount of the starting melt in the mixer goes into the inner, manufacturing scrap. If all the banks back in the form of aluminum scrap, the processing cycle circuit of old aluminum cans into new had to be replenished only by the loss of aluminum intoxication – only a few percent.

Sources:
1. Aluminum and Aluminum Alloys, ASM International, 1993
2. http://www.icaa-conference.net/ICAA12/pdf/IL-04.pdf
3. TALAT 1102
4. https://www.metalpackagingeurope.org